1. Field of the Invention
The present invention relates to an organic EL display device, in which an organic luminescent medium emits light by applying electric field thereto and color changing layers decompose and convert the light, and a method of manufacturing the organic EL display device. More particularly, the present invention relates to an organic EL display device suitably employed in display apparatuses for personal and industrial uses and the like.
2. Description of the Related Art
An organic electroluminescent (hereinafter referred to as EL) element is a natural luminescent element, which uses the principle that upon applying electric field, positively charged holes (hereinafter referred to as positive holes) injected from an anode recombine electrons injected from a cathode, and an organic luminescent medium emits light by using the combination energy.
Since C. W. Tang et al. reported an organic EL element device driven at low voltages, for example, xe2x80x9cApplied Physics Lettersxe2x80x9d, 51(12), 913, 1987, much research has been done on organic EL elements made of organic materials. Chelate complexes such as tris(8-quinolinolate)aluminum and the like, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like have been known as a luminescent material. It has been reported that they allow luminescence in the visible range form blue to red, thereby attempting the realization of a color display element.
FIG. 14 is a sectional view showing a conventional organic EL color display device.
As shown in FIG. 14, a color filter 213 is provided on a substrate 210. In the color filter 213, a plurality of color changing layers 214 are separately arranged in the order of red (R), green (G) and blue (B). Under electrodes 211 are formed in a striped pattern on the top surface of the color filter 213 along the color changing layers 214.
Upper electrodes 212 are formed in a striped pattern so as to be opposed to the under electrodes 211. An organic luminescent medium 215 is provided between the under electrodes 211 and upper electrodes 212, which medium 215 emits light when electric field is applied to the medium. In the organic luminescent medium 215, organic luminescent medium layers 215a, 215b, 215c are separately arranged so as to be substantially in a plane. The layers 215a, 215b, 215c can emit lights of three colors, R, G, B.
The layers 215a, 215b, 215c are arranged above the color changing layers 214 through the under electrodes 211 for each color so that the positions thereof coincide with those of the R, G, B color changing layers 214.
The color changing layers 214 change light to three colors, R, G, B. They enhance the color purity of the organic luminescent medium and further suppress reflection of outer light on the upper electrodes 212 and the like.
The three color organic luminescent medium layers are formed on a substrate with a mask by deposition. The low precision of positioning the mask may result in color mixture. Thus, the cost for manufacturing a highly precise display device is extremely high. Further, a pair of electrodes occur light interference. If a viewing angle changes, chromaticity changes due to the light interference.
WO98/34437 (U.S. Ser. No. 09/147,104) discloses an organic EL display device as shown in FIG. 15. In the organic EL display device, organic luminescent mediums 225 emitting mono-color light, white or blue, is placed between under electrodes 221 and upper electrodes 222; shading members 226 are interposed between color changing layers 224; and a light-transmitting medium 228 are provided between the organic luminescent mediums 225 and the color changing layers 224. The relationship d2xe2x89xa7d1 is satisfied wherein d1 represents a distance between the color changing layers 224 and the organic luminescent mediums 225, and d2 represents the width of the shading members 226.
In this organic EL display device, since the organic luminescent mediums 225 emitting mono-color light are used, the very high precision of positioning the layers 225 are not required. Further, since the above relationship d2xe2x89xa7d1 is satisfied, color mixture hardly occur, thereby improving the quality of display images.
However, the distance d1 defined by the thickness of the light-transmitting medium 228 is inevitably larger than zero. Thus, even the invention of WO98/34437 has a limitation in the precision of display and it is difficult to obtain display with high precision. Further, it is difficult that d1 is decreased to several micro meters or less, leading to high cost.
Moreover, even in the invention of WO98/34437, if a viewing angle changes, chromaticity inadvantageously changes due to light interference caused by a pair of electrodes 221, 222. In particular, since color filters are used in blue pixels when blue luminescent medium is used as an organic luminescent medium, changes in chromaticity due to light interference cannot be compensated against blue light.
An object of the present invention is therefore to provide an organic EL display device in which color mixture hardly occurs and chromaticity does not change even if a viewing angle is changed, and a manufacturing method thereof.
According to a first aspect of the present invention, there is provided an organic EL display device comprising: first electrodes and second electrodes which a voltage is applied to; conductive color changing layers capable of being electrically connected to the first electrodes; and an organic luminescent medium placed between the second electrodes and the color changing layers.
In the device of the present invention, the first electrodes, the color changing layers, the organic luminescent medium and the second electrodes may be placed in this order, and the width of the color changing layers may be substantially the same as that of the first electrodes.
Further, the first electrodes may contact the color changing layers, and the width of the first electrodes may be narrower than that of the color changing layers.
In the device of the present invention, when a voltage is applied between the first and second electrodes, electric field is generated between the second electrodes and the color changing layers in contact with the first electrodes. As a result, the organic luminescent medium emits light therebetween.
In the device of the present invention, the color changing layers may directly contact the organic luminescent medium. Alternatively, another layer such as a flattening layer may be interposed between the color changing layers and the organic luminescent medium.
Further, the first electrodes may contact the color changing layers directly or through switching elements.
The color changing layers may comprise color filters, fluorescent layers or combination thereof. The organic luminescent medium may be of mono-color emission or three-color emission type.
In the device of the present invention, since no or little light interference exists between the first and second electrodes, chromaticity does not change even if a viewing angle is changed.
Moreover, since the light from the organic luminescent medium is not or hardly obstructed by the first electrodes with a high refractive index, luminous efficiency can be enhanced.
Since the color changing layers can be placed in contact with or very close to the organic luminescent medium, color mixture due to changes in viewing angle hardly occurs.
According to a second aspect of the present invention, there is provided a method of manufacturing an organic EL display device comprising; forming conductive color changing layers and first electrodes, the color changing layers capable of being electrically connected to the first electrodes; forming an organic luminescent medium above the color changing layers; and forming second electrodes to sandwich the organic luminescent medium between the second electrodes and the color changing layers, a voltage being applied to the first and second electrodes.
Preferably, the first electrodes and the color changing layers are patterned by an etching method.
Preferably, the color changing layers are formed on the first electrodes by a micelle electrolytic method.
The present invention can be applied to organic EL display devices of bottom emission type where light is taken from a substrate or top emission type where light is taken from the direction opposite to the substrate.